Apparatus and method for generating transmission and reception local oscillation signals in a mobile terminal

ABSTRACT

There is provided an apparatus for generating a transmission of local oscillation signals and a reception of local oscillation signals in a mobile terminal. The apparatus includes: a first phase locked loop (PLL) block configured to generate a transmission local oscillation signal; a second PLL block configured to generate a reception local oscillation signal; and a controller configured to control the first PLL block to operate before a minimum time period required for the first PLL block to lock up from a start point of a transmission burst period and the second PLL block to operate before a minimum time period required for the second PLL block to lock up from a start point of a reception burst period.

PRIORITY

This application claims priority to an application entitled “Apparatusand Method for Generating Transmission and Reception Local OscillationSignals in Mobile Terminal” filed in the Korean Industrial PropertyOffice on Oct. 19, 2000 and assigned Ser. No. 2000-61478, the contentsof which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a mobile terminal, and inparticular, to an apparatus and method for generating transmission andreception local oscillation signals.

2. Description of the Related Art

In a mobile terminal, a local oscillation signal for transmission (TXlocal oscillation signal) is used to upconvert the frequency of atransmission signal, whereas a local oscillation signal for reception(RX local oscillation signal) is used to downconvert the frequency of areceived signal. The TX and RX local oscillation signals are generatedby a PLL (Phase Locked Loop) block and provided to a radio transmitterand a radio receiver, respectively.

In a conventional TDD (Time Division Duplex) mobile terminal, a TX localoscillation signal and an RX local oscillation signal are selectivelyprovided by a PLL block 8 as shown in FIG. 1. The PLL block 8synchronizes the frequency and phase of its output signal to those of areference signal or an input signal.

Referring to FIG. 1, the PLL block 8 is comprised of a frequencysynthesizer 2, a low pass filter (LPF) 4, and a voltage controlledoscillator (VCO) 6. A controller (not shown) feeds an enable signal EN,data DT, a clock signal CLK to the frequency synthesizer 2 of the PLLblock 8, so that the PLL block 8 may selectively provide: a TX localoscillation signal (TX LO) to a radio transmitter in a transmissionmode, and an RX local oscillation signal (RX LO), to a radio receiver ina reception mode. The data DT controls values for the TX and RX localoscillation signals. The frequency synthesizer 2 receives the data DT,in an active logic low state of the enable signal EN, in response to theclock signal CLK. The frequency synthesizer 2 generates a signal with avery stable frequency, by synthesizing a signal of a reference signalsource received from a reference signal generator, based on the data DT.The LPF 4 filters the signal received from the frequency synthesizer 2and provides a voltage value corresponding to the filtered signal to theVCO 6. The VCO 6 generates a signal with an oscillation frequencycorresponding to the voltage value, that is, TX LO or RX LO. TX LO andRX LO are provided to the radio transmitter and the radio receiver,respectively. Then the TX and RX oscillation signals are fed back to thefrequency synthesizer 2 at the same time.

It is possible to selectively generate a TX local oscillation signal andan RX local oscillation signal using the single PLL block 8 in theconventional TDD mobile terminal for the following reason. The TDDmobile terminal has a frame structure as shown in FIG. 2. Referring toFIG. 2, the frame is a GSM (Global System for Mobile telecommunication)TDMA (Time Division Multiple Access) frame. Each GSM TDMA frame is 4.615ms in duration and has a gap of about 1.154 ms between a TX burst periodand an RX burst period. The 1.154 ms gap is sufficient for the PLL block8 to secure a time required to switch frequencies from TX LO, and RX LO,local oscillation signals (hereinafter, referred to as “PLL lock-uptime” or “frequency switching time”). Therefore, the TDD mobile terminalcan generate TX LO in a transmission mode and RX LO in a reception modeby use of the single PLL block 8.

However, a propagation delay that occurs in a multi-time slot mode,between a mobile terminal, or between a mobile terminal and a basestation must be considered when multi-slot standards are supported as inHSCSD (High-Speed Circuit Switched Data) and GRS (General RadioService), or a satellite-based TDD scheme is employed.

The conventional mobile communication system does not need a short PLLlock-up time because it mainly provides voice transmission. On thecontrary, future mobile communication systems will be configured toadditionally provide transmission of pictures and data communication.For the resulting use of multi-time slots in a TDMA frame, the PLLlock-up time should be reduced. However, the conventional method shownin FIG. 1 has limitations in reducing the PLL lock-up time because asthe PLL lock-up time decreases, the phase noise performance of the PLLblock deteriorates.

Therefore, there exists a need for an apparatus and a method thatprovides a shorter frequency switching time, or a shorter PLL lock-uptime, which allows the PLL block to provide a transmission of picturesand data communication.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide anapparatus for generating local oscillation signals for transmission andreception in a mobile terminal that exchanges voice, images, and data.

It is another object of the present invention to provide a method forswitching frequencies between a transmission of a local oscillationsignal and a reception of a second local oscillation signal even thoughthe gap between a transmission burst period and a reception burst periodis short in a mobile terminal.

To achieve the above objects, there is provided an apparatus forgenerating a transmission of a local oscillation signal and a receptionof a second local oscillation signal in a mobile terminal, the apparatuscomprising: a first phase locked loop (PLL) block configured to generatea transmission of a local oscillation signal; a second PLL blockconfigured to generate a reception of a local oscillation signal; and acontroller configured to control the first PLL block to operate before aminimum time period required for the first PLL block to lock up from astart point of a transmission burst period and the second PLL block tooperate before a minimum time period required for the second PLL blockto lock up from a start point of a reception burst period.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become more apparent from the following detaileddescription when taken in conjunction with the accompanying drawings inwhich:

FIG. 1 is a block diagram of a PLL block utilized to generate a TX localoscillation signal and an RX local oscillation signal in a conventionalmobile terminal;

FIG. 2 illustrates the structure of a typical GSM TDMA frame;

FIG. 3 is a block diagram of a typical mobile terminal;

FIG. 4 is a block diagram of PLL blocks utilized to generate a TX localoscillation signal and an RX local oscillation signal, according to anembodiment of the present invention; and

FIG. 5 is an operational timing diagram, according to the embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be describedhereinbelow with reference to the accompanying drawings. In thefollowing description, well-known functions or constructions are notdescribed in detail since they would obscure the invention inunnecessary detail.

FIG. 3 is a block diagram of a typical mobile terminal and FIG. 4 is ablock diagram of PLL blocks utilized to generate a TX local oscillationfrequency and an RX local oscillation frequency, according to anembodiment of the present invention.

Referring to FIG. 3, there is a typical mobile terminal. The mobileterminal is comprised of a controller 100, a memory 102, a keypad 104, adisplay 106, an antenna 108, a RF (Radio Frequency) Module 110, aBaseband Processor 112, a CODEC (Coder-Decoder) 114, an amplifier 116, amicrophone 118, a speaker 120, a ringer 122 and a vibrator 124.Controller 100 is connected to: memory 102, keypad 104, display 106, RF(Radio Frequency) module 110, baseband processor 112, CODEC(Coder-Decoder) 114 AND amplifier 16. In addition, controller 100processes a normal telephone call or data communication and processes avoice signal and data for wireless Internet access, according to acorresponding protocol. Further, controller 100, instructs eachcomponent of the mobile terminal. The memory 102 includes a ROM (ReadOnly Memory), a flash memory, and a RAM (Random Access Memory). The ROMstores operation and control programs and data for the controller 100.The RAM provides a working memory for the controller 100. The flashmemory provides an area for storing updatable data.

The keypad 104 has a plurality of keys including digit keys and providesa key input signal to the controller 100. The display 106 usuallyincludes an LCD (Liquid Crystal Display), which, displays informationunder the control of the controller 100. The RF module 110 receives anRF signal from a base station via an antenna 108, then converts thereceived RF signal to an IF (Intermediate Frequency) signal, and outputsthe IF signal to the baseband processor 112. The RF module 110 alsoconverts an IF signal received from the baseband processor 112 andtransmits the RF signal to the base station. The baseband processor 112is a baseband analog application specific integrated circuit (BBA) thatinterfaces the controller 100 to the RF module 110. The basebandprocessor 112 converts a digital baseband signal received from thecontroller 100 to an analog IF signal. Then the baseband processor feedsthe analog IF signal to the RF module 110. Baseband processor 112 alsoconverts an RF signal to an analog IF signal received from the RF module110 to a digital baseband signal, then feeds the digital baseband signalto the controller 100. The CODEC 114 is connected to a microphone 118and a speaker 120 through amplifier 116. The CODEC 114 PCM (Pulse CodeModulation)—encodes a voice signal received from the microphone 118,then outputs the voice data to the controller 100. CODEC 114 PCM-decodesvoice data received from the controller 100, then outputs the voicesignal to the speaker 120 via the amplifier 116. The amplifier 116amplifies a received voice signal or a voice signal to be transmitted tothe speaker 120 and adjusts the volume of the speaker 120 and the gainof the microphone 118 while under the control of the controller 100. Aringer 122 generates a bell sound under the control of the controller100, and a vibrator 124, under the control of the controller 100,generates vibrations.

The RF module 110 includes a first PLL block 18, and a second PLL block28 as shown in FIG. 4, according to the embodiment of the presentinvention. The controller 100 controls the PLL blocks 18 and 28.

Along with the recent trend of transmission of pictures and data, aswell as voice transmission, multi-time slots are used in a data frame.Therefore, a gap between a transmission burst period and a receptionburst period is narrowed. This implies that it is difficult to secure aPLL lock-up time required for a PLL to switch a TX local oscillationsignal to an RX local oscillation signal. Unless the PLL lock-up time issecured, phase noise characteristics are deteriorated.

Since there is a limit in reducing the PLL lock-up time by use of asingle PLL, the two PLL blocks 18 and 28 are provided in the embodimentof the present invention. By controlling the PLL blocks 18 and 28 withthe controller 100, the PLL lock-up time is definitely secured.

Referring to FIG. 4, the first PLL block 18 generates a TX localoscillation signal to a radio transmitter and the second PLL block 28generates an RX local oscillation signal to a radio receiver. Thecontroller 100 instructs the first PLL block 18 to operate in a timeshorter than a minimum time required for the PLL to lock up block 18from the starting point of a transmission burst period. In addition,controller 100 instructs second PLL block 28 to operate in a timeshorter than a minimum time required for the PLL block 18 to lock upfrom the starting point of a reception burst period.

A first frequency synthesizer 12, a first LPF 14, and a first VCO 16 inthe first PLL block 18 and a second frequency synthesizer 22, a secondLPF 24, and a second VCO 26 in the second PLL block 28 operate in thesame manner as their counterparts in FIG. 1. Thus, the components of thefirst and second PLL blocks 18 and 28 are not described here.

The controller 100 applies a data DT and a clock signal CLK to both thefirst frequency synthesizer 12 and the second frequency synthesizer 22,according to the embodiment of the present invention. The controller 100applies a transmission enable signal EN_TX to the first frequencysynthesizer 12 and a reception enable signal EN_RX to the secondfrequency synthesizer 22.

FIG. 5 is an operational timing diagram of the transmission enablesignal EN_TX, the reception enable signal EN_RX, the clock signal CLK,and the data DT provided by the controller 100, according to theembodiment of the present invention.

The operation of the PLL blocks, according to the embodiment of thepresent invention, will be described in detail referring to FIGS. 3, 4,and 5.

As shown in FIG. 5, the narrowest gap between a transmission burstperiod 30 and a reception burst period 32 by 9 symbols, is about 500μsec. The 500 μsec gap is too short to be a PLL lock-up time. Therefore,the controller 100 controls the PLL blocks 18 and 28 to have asufficient PLL lock-up time according to the embodiment of the presentinvention.

To do so, the controller 100 instructs the first PLL block 18 to operatebefore a minimum time P1 required for the first PLL block 18 to lock upfrom the start point, St, of the transmission burst period 30, that is,at a time point t1. Specifically, the controller 100 shifts thetransmission enable signal EN_TX to an active low state, at the timepoint t1, and provides the clock signal CLK. The data DT correspondingto the frequency of a TX local oscillation signal, TX LO, is provided tothe first PLL block 18 for a period when the transmission enable signalEN_TX is in the active logic low state. As a result, the first PLL block18 generates the TX LO, in response to the data DT and the clock signalCLK. Even for the minimum time P1 required for the first PLL block 18 tolock up, the first PLL block 18 generates TX LO and provides it to theradio transmitter of the RF module 110. Since the radio transmitter isdisabled in a non-transmission burst period, the generation of the TX LOfor the time period P1 has no influence on the operation of the mobileterminal.

According to another embodiment of the present invention, the controller100 instructs the first PLL block 18 to operate before the end point ofthe reception burst period 32, for example, near the time point t1.

To operate the second PLL block 28 with a sufficient PLL lock-up time,the controller 100 instructs the second PLL block 28 to operate before aminimum time P2 required for the second PLL block 28 to lock up from thestarting point, Sr, of the reception burst period 32, that is, at a timepoint t2. Specifically, the controller 100 shifts the reception enablesignal EN_RX to an active low state at the time point t2 and providesthe clock signal CLK. The data DT corresponds to the frequency of an RXlocal oscillation signal RX LO is provided to the second PLL block 28for a period when the reception enable signal EN_RX is in the activelogic low state. As a result, the second PLL block 28 generates RX LO inresponse to the data DT and the clock signal CLK. Even for the minimumtime P2 required for the second PLL block 28 to lock up, the second PLLblock 28 generates RX LO and provides it to the radio receiver of the RFmodule 110. Since the radio receiver is disabled in a non-receptionburst period, the generation of RX LO for the time period P2 has noinfluence on the operation of the mobile terminal.

It is further contemplated as another embodiment of the presentinvention that the controller 100 instructs the second PLL block 28 tooperate before the end point of the transmission burst period 30, forexample, in the vicinity of the time point t2.

As described above, the gap (e.g., 500 μsec) between the transmissionburst period and the reception burst period and some time (e.g., αseconds) before the gap period are given as a PLL lock-up time so that aPLL has a sufficient lock-up time in the present invention. Hence,without increasing the PLL lock-up time, PLL phase noise characteristicscan be optimized.

Table 1 shows the relationship between a PLL lock-up time and phasenoise as measured in a mobile terminal for communication of voice,pictures, and data.

TABLE 1 test condition unit phase noise frequency offset 1.0 −70 −71.0dBc/Hz 5.0 −66.0 −69.0 12.5 −71.0 −78.0 25.0 −80.0 −88.0 50.0 −90.0−98.0 100 −101.0 −109.0 lock-up time 500 800 μsec

As noted from Table 1, phase noise is very different, according tolock-up time 500 μsec and 800 μsec under the same conditions. It can beconcluded that application of the present invention stabilizes theoperation of a PLL block when phase noise characteristics do not come upto a specification, or a margin between the phase noise characteristicsand the specification is not enough.

In accordance with the present invention as described above, a PLL canbe lock up more steadfastly in a TDD mobile terminal, especially amobile terminal requiring a short PLL lock-up time, and the mobileterminal can be designed such that the phase noise characteristics of aPLL block are reflected. While the conventional PLL scheme is limited inincreasing a PLL lock-up time to satisfy a given phase noisespecification due to the relation between the PLL lock-up time and phasenoise, the PLL lock-up time can be increased without influencing phasenoise characteristics.

While the invention has been shown and described with reference tocertain preferred embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and detail may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims.

1. An apparatus for generating transmission local oscillation signalsand reception local oscillation signals in a mobile terminal,comprising: a first phase locked loop (PLL) block configured to generatea transmission local oscillation signal; a radio transmitter portion forreceiving the transmission local oscillation signal; a second PLL blockfor generating a reception local oscillation signal; a radio receptionportion for receiving the reception local oscillation signal; and acontroller configured to control the first PLL block to operate before aminimum time period required for the first PLL block to lock up from thestart point of a transmission burst period, to control the second PLLblock to operate before a minimum time period required for the secondPLL block to lock up from the start point of a reception burst period,to control the radio transmitter portion to operate only during atransmission burst period and to control the radio reception portion tooperate only during a reception burst period.
 2. An apparatus forgenerating a transmission local oscillation signal and a reception localoscillation signal in a mobile terminal, comprising: a first PLL blockconfigured to generate the transmission local oscillation signal; aradio transmitter portion for receiving the transmission localoscillation signal; a second PLL block configured to generate thereception local oscillation signal; a radio reception portion forreceiving the reception local oscillation signal; and a controller forcontrolling the first PLL block to operate before an end point of areception burst period, for controlling the second PLL block to operatebefore an end point of a transmission burst period, for controlling theradio transmitter portion to operate only during a transmission burstperiod and for controlling the radio reception portion to operate onlyduring a reception burst period.
 3. A method of generating atransmission local oscillation signal and a reception local oscillationsignal in a mobile terminal having a first PLL block for generating thetransmission local oscillation signal and a second PLL block forgenerating the reception local oscillation signal, comprising:controlling the first PLL block to operate before a minimum time periodrequired for the first PLL block to lock up from the start point of atransmission burst period; controlling a radio transmitter portion tooperate only during a transmission burst period; controlling the secondPLL block to operate before a minimum time period required for thesecond PLL block to lock up from the start point of a reception burstperiod; and controlling a radio reception portion to operate only duringa reception burst period.
 4. The method of claim 3, further comprising:applying the reception local oscillation signal generated from thesecond PLL block to a radio receiver for the reception burst period; andapplying the transmission local oscillation signal generated from thefirst PLL block to the radio transmitter for the transmission burstperiod.
 5. A method of generating a transmission local oscillationsignal and a reception local oscillation signal in a mobile terminalhaving a first PLL block for generating the transmission localoscillation signal and a second PLL block for generating the receptionlocal oscillation signal, the method comprising: controlling the firstPLL block to operate before the end point of a reception burst period;controlling a radio transmitter portion to operate only during atransmission burst period; controlling the second PLL block to operatebefore the end point of a transmission burst period; and controlling aradio reception portion to operate only during a reception burst period.6. The method of claim 5, further comprising: applying the receptionlocal oscillation signal generated from the second PLL block to a radioreceiver for the reception burst period; and applying the transmissionlocal oscillation signal generated from the first PLL block to a radiotransmitter for the transmission burst period.